【leetcode】284. Peeking Iterator

题目：
Given an Iterator class interface with methods: next() and hasNext(), design and implement a PeekingIterator that support the peek() operation – it essentially peek() at the element that will be returned by the next call to next().

思路：
把下一个元素值以及其存在状态提前保存起来。

代码实现：

/** Below is the interface for Iterator, which is already defined for you.* **DO NOT** modify the interface for Iterator.**  class Iterator {*		struct Data;* 		Data* data;*		Iterator(const vector& nums);* 		Iterator(const Iterator& iter);** 		// Returns the next element in the iteration.*		int next();**		// Returns true if the iteration has more elements.*		bool hasNext() const;*	};*/class PeekingIterator : public Iterator {
public:int next_elem;bool next_exist;PeekingIterator(const vector<int>& nums) : Iterator(nums) {// Initialize any member here.// **DO NOT** save a copy of nums and manipulate it directly.// You should only use the Iterator interface methods.if (Iterator::hasNext()){next_elem = Iterator::next();next_exist = true;}else{next_exist = false;}}// Returns the next element in the iteration without advancing the iterator.int peek() {return next_elem;}// hasNext() and next() should behave the same as in the Iterator interface.// Override them if needed.int next() {int ret = next_elem;if (Iterator::hasNext()){next_elem = Iterator::next();next_exist = true;}else{next_exist = false;}return ret;}bool hasNext() const {return next_exist;}
};

参考：
https://leetcode.com/problems/peeking-iterator/discuss/72598/Another-C%2B%2B-solution-with-one-line-in-peek()-and-hasNext()-AC

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